Interest in fuel cell batteries as power sources for portable electronic devices has grown. A fuel cell is an electrochemical cell that uses materials from outside the cell as the active materials for the positive and negative electrode. Because a fuel cell does not have to contain all of the active materials used to generate electricity, the fuel cell can be made with a small volume relative to the amount of electrical energy produced compared to other types of batteries.
In some types of hydrogen fuel cells, hydrogen is formed from a hydrogen-containing fuel supplied to the negative electrode side of the fuel cell. In other types of hydrogen fuel cells, hydrogen gas is supplied to the fuel cell from a source outside the fuel cell.
A fuel cell system can include a fuel cell battery, including one or more fuel cells (e.g., a fuel cell stack), and a fuel source, such as a fuel tank or a hydrogen generator. Hydrogen generators that supply hydrogen gas to a fuel cell can be an integral part of a fuel cell system, or they can be removably coupled to the fuel cell system. A removable hydrogen generator can be replaced with another one when the hydrogen containing materials have been consumed. Removable hydrogen generators can be disposable (intended for only a one-time use). Both removable and permanently installed hydrogen generators can be refillable (intended for use multiple times) to replace consumed fuel composition.
Hydrogen generators can produce hydrogen using a variety of hydrogen containing materials and a variety of methods for initiating the hydrogen generating reactants. Hydrogen gas can be released when a hydrogen containing material is heated.
In selecting hydrogen containing materials for use in a hydrogen generator, consideration may be given to the following: (a) stability during long periods of time when the hydrogen generator is not in use, (b) ease of initiation of a release of hydrogen gas, (c) the amount of energy that must be provided to sustain the release of hydrogen gas, (d) the maximum operating temperature of the release of hydrogen gas, and (e) the total volume of hydrogen that can be produced per unit of volume and per unit of mass of the hydrogen containing material(s).
Some hydrogen containing compounds can be heated to release hydrogen gas, such as in a chemical decomposition reaction. Reactants that can undergo thermal decomposition reactions to produce hydrogen gas are desirable because they generally produce a relatively high volume of hydrogen gas on a volumetric basis.
One problem with conventional hydrogen generators is that heat transfer from the heater to the fuel is inefficient. Another problem with conventional hydrogen generators is difficulty in loading and unloading fuel units and replacing spent fuel units without damaging the hydrogen generator or the fuel unit.